1. Field of the Invention
This invention is related to a cutter bit that is used for the impingement of substrate for earth strata such as, for example, asphalted roadway surface, coal deposits, and mineral formations. More specifically, the invention relates to a cutter bit having a hard tip insert protruding therefrom, wherein the insert has an offset apex.
2. Description of Related Art
A cutter bit for use in mining or construction applications typically has a generally elongated cylindrical geometry. Such a cutter bit comprises an elongated steel cutter bit body which has an axially forward end and an opposite axially rearward end. A cutter insert of hard or super hard material typically affixes to the axial forward end of the cutter bit body. The cutter bit body typically is rotatably or non-rotatably secured to a stationary block or holder on a drum.
Cutter bits experience wear in a number of ways due to the environment in which they operate and must be frequently replaced. It is highly desirable to provide an improved cutter bit that experiences an increase in useful tool life as compared to heretofore known cutter bits.
FIG. 1 illustrates a portion of a continuous mining machine 10 comprised of a rotatable shaft 12 having a first sprocket 14 and an associated drive chain 15 which is driven by a second sprocket 17. Attached to the drive chain 15 are a plurality of cutter links 20 each containing a cutter bit 25. Each cutter bit 25 has an insert 27 which contacts earth strata S or road pavement to break up material for removal. During the operation, as the insert 27 moves through the substrate S a force FR is applied to the insert 27. Typically, the force FR acts upon the cutter insert 27 along a line that forms an angle X with the central longitudinal axis 32 of the cutter body 30 of between 5-20°. FIG. 2 is a portion of FIG. 1 enlarged to show details of the cutter bit 25. As illustrated in FIGS. 2 and 3, when the force FR is applied to the insert 27 there is a region U behind the insert 27 that is unsupported. Directing attention to FIG. 3, typically, the cutter bit 25 is comprised of the body 30 having a central longitudinal axis 32 extending therethrough. An insert holder 35 is secured to the body 30 and the insert 27 is secured within the insert holder 35. Typically, the insert 27 has a cemented carbide body with a conical tip 28. The insert holder 35 is carbide such that the insert 27 may be brazed into the holder 35. Such a cutter bit is disclosed in United States Patent Application Publication No. US 2012/0242136, which is hereby incorporated herein in its entirety.
Returning to FIG. 3, typically the resultant force FR is broken into an axial component FA parallel to the central longitudinal axis 32 and a lateral component FL perpendicular to the central longitudinal axis 32. Because the region U is unsupported, the lateral force FL applies an undesirable bending moment to the cutter insert 27. While the inserts are typically made of cemented carbide, they may also be made of other super hard materials. Each of these materials has a very high compressive strength but a relatively low tensile strength. As a result, a design is sought to provide additional support to the insert against the lateral force acting upon it to minimize bending moments caused by the lateral force. Additionally, in other prior art designs, the conical tip of the cutter insert 27 was not made of cemented carbide, but was made entirely of PCD (polycrystalline diamond) to compensate for the unsupported region U of the insert 27. A design is sought that would eliminate or reduce the amount of PCD used in these inserts 27.